enum QGraphicsPixmapItem::ShapeMode

The shape is determined by calling QPixmap::mask(). This shape includes only the opaque pixels of the pixmap. Because the shape is more complex, however, it can be slower than the other modes, and uses more memory.

QGraphicsPixmapItem::BoundingRectShape

1

The shape is determined by tracing the outline of the pixmap. This is the fastest shape mode, but it does not take into account any transparent areas on the pixmap.